It becomes confusing when trying to size trolling motors because they are based on pounds of thrust instead of horsepower, which is the traditional measure.
The words horsepower and thrust are used interchangeably by many boaters. This is incorrect, as the two terms refer to different motor characteristics.
A car with high torque levels can accelerate faster but generally have a reduced top speed. The same applies to a trolling motor on a boat.
Where the higher thrust levels do not produce higher speed but rather maintain the position of a heavier boat or one moving through a current.
At a Glance:
1️⃣ The weight of the boat is the most critical factor when determining the appropriate thrust of a trolling motor. As a general guideline, 2 lbs. of thrust is required for every 100 lbs. of boat weight.
2️⃣ The amount of voltage required by the motor also significantly affects the thrust produced. More voltage generally means greater thrust, and this will influence the number of 12-volt batteries you need.
3️⃣ The desired trolling speed and the type of fishing you intend to do should also be considered when deciding on a trolling motor.
Ultimately your choice of motor will be different if you fish in strong winds or currents than if you are targeting species in calmer water conditions, like inland lakes. Now let’s turn the conversation to thrust factors.
🚀 The Factors To Consider When Defining The Trolling Motors Thrust
The following factors will determine the right trolling motor for your boat.
The Boat Weight
The boat’s weight is the most important variable when considering the trolling motor’s thrust. As a principal, you can never have too much thrust but can easily have too little.
As an overall guide, 2 lbs. of thrust is required to power every 100 lbs. of boat weight (fully loaded).
For example, 2,750 lbs. boat = (2,750lb / 100) x 2 = 55 lbs. of thrust (minimum.)
The size of the motor is calculated as follows to move a boat that weighs twice the amount at the same speed.
5,500 lbs. boat = (5,500 lbs. /100)*2 = 110 lbs. of thrust.
The Voltage Required
Another important variable in the mix is the number of 12-volt batteries you need.
The higher the voltage available for the motor, the greater the thrust produced.
The general rule is listed below. I’ve linked another article about what different voltage means in trolling motors if you are interested.
|Thrust Level||Voltage||No Of Batteries|
|Thrust 55 Lbs. Or Less||12 volt||1|
|55 Lbs. To 80 Lbs.||24 volt||2|
|101 Lbs. To 112 Lbs.||26 volt||3|
What Is The Desired Trolling Speed?
The trolling speed will depend on where you fish and what type of bait (lure) you use.
The rule of thumb which is generally applied is as follows.
1️⃣ Crankbaits have the best action when being towed at 1.8 mph.
2️⃣ Jerk baits have the best action when being towed at 2.4 mph.
The speeds may differ in the waters you fish in and the species you fish for, so you should test different speeds to determine the correct speed in your circumstances.
You must add thrust to the equation if you fish in conditions with a strong wind or current.
You will never be disappointed having more thrust than the conditions required but having too little can spoil a day on the water.
Remember, thrust does not equate to more speed, but it does provide you with the ability to hold a position in strong currents or higher winds.
The Amount Of Space Available For The Battery
Consider how much space is available in the boat (possibly in the bilge) is available to store the batteries. On some motors, three 12-volt batteries will be required, which take up a lot of space.
🏋️♂️ Thrust You Need For Different Boat Weights
The list below provides the minimum trolling motor specifications for different boat weights measured in pounds. For interest’s sake, here is the most powerful electric trolling motor available.
|Boat Weight (Lbs.)||Boat length||Required Thrust Level||Batteries Required||Amps||Watts||EquivHP|
|Kayaks and canoes||10 – 13||30 Lbs.||12 Volt||33.00||396||0.5|
|1,500 – 2,000 Lbs.||14 – 18||40 Lbs.||12 Volt||44.00||528||0.7|
|2,001 – 2,500 Lbs.||19 – 21||50 Lbs.||12 Volt||55.00||660||0.9|
|2,501 – 3,500 Lbs.||22 – 23||70 Lbs.||24 Volt||77.00||1848||2.5|
|3,501 -4,500 Lbs.||24 – 25||80 Lbs.||24 Volt||88.00||2112||2.8|
|4,501 Lbs. And Higher||26 plus||105 Lbs.||36 Volt||115.50||4158||5.6|
📑 How Do You Apply The Results Of This Table?
The practical applications of this are as follows.
Trolling Motor Sizes For Kayaks
The ideal amount of thrust a trolling motor produces for kayaks will depend on the kayak’s weight.
The smallest sized trolling motor (30 lbs. thrust) will work acceptably for Kayaks weighing between (with passenger and stores) 500 lbs. and 1,500 lbs.
Remember this is a minimum specification; if conditions require, a 50 lbs. thrust motor may be needed.
Trolling Motor Sizes For Jon Boats
The thrust required will depend on the Jon boat’s shaft length and weight. Learn about [long shaft trolling motors] and their effect on thrust capabilities.
Even though the Jon boat may only be 15 feet long, if it is loaded up to the gunnels with equipment and three burly anglers are on board, it will need a higher rating than the table may indicate.
If the boat weighs 2,000 lbs. or less (with occupants and equipment) and is used in calm waters, a 40 lbs. trolling motor will be adequate. A higher thrust motor will be required as soon as these limits are exceeded.
Trolling Motor Sizes For Pontoon Boats
Once again, the pontoon’s size and loaded weight will determine the size of the motor which is fitted.
The dry weight (i.e., the weight with no stores, batteries, and passengers) of pontoons ranges between 1,200 lbs. and 2,800 lbs.
Add nine passengers (180 lbs. average) the weight increases by 1,620 lbs.
Add 3 batteries and stores, plus stores increase the weight by 500 lbs.
This equates to 3,320 lbs. and 4,820 lbs.
These will require a motor ranging from 70 lbs. 105 lbs.
Does Higher Thrust Mean Higher Speed?
Horsepower is a measure of “work” produced by an engine, while thrust is the measure of static force the engine produces. If that seems as clear as mud, the following may help!
Horsepower is the measure normally applied to gas-powered engines and is a measure of work governed by three variables. Namely Force, Distance, and Time.
The force needed to propel an object weighing 550 pounds over a distance of 1 foot in just 1 second is defined as one horsepower. This is equivalent to 746 watts.
An electric trolling motor is generally defined by the “pounds of thrust” it produces.
The size and weight of the boat will determine how much thrust is needed to produce a satisfactory speed on the water.
The larger the boat (and therefore, the heavier it is), the higher the thrust to move the boat at the same speed as smaller boats.
Horsepower Compared To Thrust
Because the two measures compare different metrics, they cannot be compared with an adjustment applied. It’s important to comprehend the connection between thrust and horsepower when considering trolling motor performance.
To calculate the horsepower of an electric trolling motor, you need to measure the watts used by the motor.
To calculate the watts, you need to know the amps drawn when the motor operates at top speed. (a measure of the number of electrons passing a specified point in a circuit in 1 second).
These must be converted into watts.
The manufacturer normally provides the amps used at top speed in the motor spec sheet.
The formula to calculate watts is Amps x Volts = Watts.
For this example, we will calculate the horsepower of an electric motor producing 55lb of thrust, drawing 52 amps at full speed, and using a single 12V battery.
52 (amps) X 12 (Volts) = 624 (watts)
Therefore, if one horsepower equals 746 watts, the horsepower of our theoretical motor equals.
624/746 = 0.83 horsepower.
As discussed above, thrust is a measure of the force applied. This means that it is not a measure of speed. An engine producing high thrust ratings may not turn the propeller any faster.
How Fast Will A 55 Lbs Thrust Trolling Motor Go?
The amount of thrust a trolling motor produces is not determined by the thrust level.
Most trolling engines can propel the boat at +- 5 mph. A higher-powered trolling motor will use less energy to achieve this and, consequently, less battery power.
How Fast Will A 40 Lbs Thrust Trolling Motor Go?
Once again, while a 40 lbs. motor may be able to propel the boat at 5 mph, it will need higher power levels to do so and will therefore use up the battery faster.
How Fast Will A 100 Lbs Thrust Trolling Motor Go?
The same rule applies to a 100-pound motor. The benefit of using a 100-pound motor on the same size boat will be that the battery will last longer.
In addition, if the boat is used in windy conditions or there is a string current, the larger thrust-size motor will be able to maintain the desired course more easily while using less energy.
🔑 Key Takeaways
As this trolling motor thrust guide explains, thrust and horsepower are different measurements, and each is used for different purposes when calculating the size motor needed for a boat.
1️⃣ The thrust required for different types of boats like kayaks, jon boats, and pontoon boats varies depending on the boat’s weight, including passengers and stores. More substantial and heavier boats will generally require motors with higher thrust levels.
2️⃣ While higher thrust does not directly equate to higher speed, it does help maintain position in strong currents or winds, and it allows for more efficient battery use. However, your speed on the water is generally not determined by the thrust level.
3️⃣ The space available for batteries in your boat is a practical consideration, as more powerful motors will require more batteries. As such, it’s important to balance your need for thrust with the available space on your boat.